The invention relates to a cylinder drum for a hydrostatic piston engine, having at least one kidney-shaped control port/cylinder bore transition which leads into a cylinder bore for receiving a piston that can be axially displaced therein.
Publication DE 43 41 846 C1 makes known a hydrostatic piston engine that includes a cylinder drum in which at least one cylinder bore is formed, in which a piston can be moved upwardly and downwardly. The motion of the piston is controlled by a swash plate against which the piston bears with the aid of a sliding block. The cylinder drum has a contact surface on the end face out of which the piston does not extend; the cylinder drum bears via the aforementioned contact surface against a valve plate. Two kidney-shaped control ports are formed in the valve plate. One kidney-shaped control port is designed as an inlet opening, while the other kidney-shaped control port is designed as an outlet opening. A kidney/cylinder bore transition is formed in the cylinder drum between the cylinder bore and the contact surface on the end face of the cylinder drum out of which the piston does not extend. When the cylinder drum rotates about its rotational axis, the contact surface of the cylinder drum glides across a diametrically opposed contact surface of the valve plate. The kidney/cylinder bore transition alternately connects the cylinder bore to the inlet opening which is connected to a suction connection when a pump is present, and to the outlet opening which is then connected to a pressure connection. When the piston moves downward in the cylinder bore, hydraulic fluid is pumped through the kidney/cylinder bore transition into the cylinder bore. When the piston moves upward, hydraulic fluid is pumped out of the cylinder bore through the kidney/cylinder bore transition out of the cylinder bore. The cylinder drum that was disclosed has the disadvantage that, when the piston moves downward in the cylinder bore, only a relatively small quantity of hydraulic fluid is pumped into the cylinder bore. Therefore, at a given pivot angle of the swash plate per revolution of the cylinder drum, only a relatively small quantity of hydraulic fluid can be pumped from one kidney-shaped control port to the other kidney-shaped control port.